In the photographic process, an image-wise exposed film must be processed to convert the latent image into a viewable negative of the image. The processing operation requires a development step, wherein the exposed silver halide crystals are reduced to elemental silver, and a fix or bleach step wherein the unexposed silver halide crystals are removed from the film. It is also advantageous to wash the film prior to drying and viewing.
Development is accomplished by the reduction of exposed silver halide to silver metal. When hydroquinone, or an equivalent, is used as the reducing agent the reaction which occurs is represented by Equation 1. EQU 2AgBr+HO-C.sub.6 H.sub.4 -OH+Na.sub.2 SO.sub.3 .fwdarw.2Ag+HO-C.sub.6 H.sub.4 -OSO.sub.3 Na+HBr+NaBr 1
The active ingredients, hydroquinone and sodium sulfite, are depleted by the silver reduction reaction. Because of the chemical depletions the effectiveness of the processing solution decreases with use. Also occuring is an increase in the bromide level and a decrease in the pH.
Ascorbic acid based developers are also used for reduction of exposed silver halide during development. Analogous depletion of active ingredients is observed with use.
Methods of replenishing the active ingredients are well known in the art and most modern processors are equipped with tanks of replenishment solution and an automatic replenishment mode based on various criteria as known in the art.
Hydroquinone developers are also susceptible to air oxidation. The chemical reaction associated with air oxidation is provided in Equation 2. EQU HO-C.sub.6 H.sub.4 -OH+2Na.sub.2 SO.sub.3 +O.sub.2 .fwdarw.HO-C.sub.6 H.sub.4 -O-SO.sub.3 Na+Na.sub.2 SO.sub.4 +NaOH 2
Air oxidation of a hydroquinone developer does not effect the bromide level but the pH increases due to liberation of hydroxide ion as the sodium salt.
Evaporation of water is also known to occur. Loss of solvent can alter the concentration of ingredients and the reactivity. Yet another detrimental phenomenon is the physical removal of developer solution by the film.
Under standard operating conditions decreases in developer activity are expected due to the development reaction, oxidation reaction, solvent evaporation and physical removal. All of these detrimental phenomenon occur, albeit at different rates. When a large amount of film is processed the development reaction is dominant and the problems which must be addressed are decreasing active ingredients, increasing bromide and decreasing pH. When a small amount of film is processed, or for periods of inactivity, the oxidation reaction and solvent evaporation are the dominant concerns.
Monitoring the bromide in the developer is advantageous for suggesting hydroquinone depletion as detailed in U.S. Pat. Nos. 3,529,529 and 3,970,457 yet oxidation is not addressed with this method. In practice these automatic systems are known to fail which is blamed, in part, on the lack of an effective method for standardizing electrodes that are continuously monitored. Monitoring pH is not considered to be effective since competing development and oxidation reactions could balance with no substantial change in pH. Also, most modern developer solutions contain pH buffers which may mask changes. Monitoring both bromide and pH places a burden on the user and is typically neither feasible nor diagnostic.
Specific gravity is another analytical measurement which is often used during the initial makeup of the solutions. The inaccuracy and non-specificity of this method is well known in the art and diagnostic information is rarely obtained.
There has been a long felt need in the art to provide a diagnostic measurement whereby the chemicals and their replenishment can be optimized. Prefered is a single measurement which can provide the diagnositic information.
The prior art also suffers from the lack of diagnostic information provided by the above mentioned measurements. For example, a high bromide ion concentration in the developer would suggest more replenishment chemicals need to be added as described for hydroquinone systems in U.S. Pat. Nos. 3,529,529 and 3,970,457. If oxidation, or evaporation, has occured in the replenishment solution, or if the replenisher is incorrectly prepared the bromide ion concentration alone may provide an inaccurate assessment of developer strength.
The ineffective quantitative means of determining chemical activity has led to the design of indirect methods to determine chemical activity of the developer. The standard method in the art has been to process film and monitor the photographic response as detailed in U.S. Pat. Nos. 5,063,583; 4,508,686 and 4,365,895. A similar approach has been adopted by the American College of Radiology and is manifested in their recommendations for accreditation under the processing section of their Mammography Accreditation Program. These methods are all predicated on the assumptions that:
(a) the film samples are identical and stable with time; PA1 (b) exposure and density readings are invariant; PA1 (c) the developer used at the start of the test is correct; and PA1 (d) changes in chemistry will have a predictable, or noticeable, effect on the film. In actual practice all of these assumptions may, and do, fail. PA1 (a) contacting exposed silver halide film with a developer comprising two compounds wherein the concentration of the two compounds is known prior to said contacting, wherein the concentration of each of the two compounds can be quantitatively determined in a simple potentiometric titration with silver nitrate and wherein the reduction to silver causes depletion of one of the two compounds; PA1 (b) titrating depleted developer which results from reduction of exposed silver halide to silver with silver nitrate with the proviso that only a single titration takes place; PA1 (c) adding an additional quantity of each of said two compounds to depleted developer based on the titration in step (b) resulting in the same concentration of developer compared to an initial developer concentration in step (a); and PA1 (d) contacting additional exposed silver halide film with the developer resulting from step (c) to reduce exposed halide film to silver.
The choice of film is also critical as realized in the art. Films which utilize tabular grains are known to exhibit sensitometric properties which vary with bromide level in the developer. Films with more conventional grains are known to be less sensitive to bromide level but sensitometric differences correlate more strongly to processing temperature and other changes in developer. This places a burden on the health care professional since different films could exhibit different properties in the same processor. To adequately use the indirect method a control film would have to be established for all types of films employed.
A particular deficiency of prior art tests is the lack of information on the activity of the replenisher chemicals. The bromide titration, or indirect film methods, only test the activity of the development solutions in the processor at the time of the test. A single test provides no information about the replenishment conditions. To obtain information on replenishment a subsequent test must be done and the data correlated to analyze for trends and/or the replenisher must be checked independently. Furthermore, a film method is intrusive since the test film itself initiates the development reaction and some replenishment occurs to compensate therefor. Immediately after the control film is processed the conditions in the development solution will be different.
An improperly prepared replenisher may take a considerable amount of time (several hours to several days) to displace a sufficient amount of developer to be observed by a film test. Nominal replenishment rates, as expected for moderate film use, are sufficient to replace approximately half of the chemicals in the developer tank with replenisher chemicals in approximately 8-10 hours. The full effect of incorrect replenishment, either rate or composition, may not be noticed until the developer has been replaced by at least one equal volume of replenisher. This creates a lag time between replenisher preparation, or a change in the rate of addition, and the actual sensitometric effect. The lag time can span several days in some instances. Once an actual problem is detected the entire replenisher and developer must be replaced to correct the situation.
It is not uncommon that specific chemical changes combine with film choice to generate a rapidly deteriorating problem. If the film is particularly sensitive to specific changes in chemistry a deterioration in performance may occur from the time the new replenisher is prepared. The deterioration in performance may not be realized for quite some time, particularly when large batches of film are processed. This problem is especially troublesome in cases such as mammographic exams where mobile units acquire the exposed films and return to a central processing center wherein all of the films are processed prior to being observed.
The tardiness of the test is especially critical if recommended procedures are followed in entirety. Corrective action is suggested only after three consecutive test are observed to generate a trend in any direction away from the norm. Typical test frequency is daily for most situations but the actual time can vary substantially. Therefore, many inferior films could be produced prior to running a control which may lead to an incorrect diagnosis or a need to repeat the exposure to the patient.
Faced with this chemical dilemma and the accepted American College of Radiography guidelines, the practitioner is forced into one of the following two situations. The first is a correct film measurement indicating the current chemistry may be correct but replenishment conditions are unknown. In this situation the practitioner typically continues operating with no knowledge of potential problems. The second situation occurs when the film measurements are not correct. Based on the standard guidelines an initial check of obvious problems such as temperature, and the like, is suggested. If the problem is not resolved the processing and replenishment chemicals are usually discarded and replaced at a substantial financial and time burden to the medical professional.
There is a long felt need in the art to provide means for improved quality control in film processing. There is a further need to provide a developer and replenisher therefore which purposefully contain ingredients that can be accurately and rapidly analyzed to determine the chemical activity of the solution. Described herein is a chemical development method wherein specific ingredients can be added and a potentiometric titration performed to insure proper levels of developer, replenisher, color chromophores and the like.
It is an object of the present invention to provide an improved development method for silver halide films which can be easily monitored and can provide diagnostic information on the activity of the developer.
It is a further object to provide a developer solution, and replenisher therefore, which can provide diagnostic information on the activity of the developer and the replenisher from a single measurement.
It is a further object that the developer/replenisher solution can be monitored independent of the film thereby decreasing the effects of film, exposure and density measurements on the development conditions.